Post on 27-Dec-2015
transcript
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Te-Yuan Huang, Kuan-Ta Chen, Polly Huang
Network and Systems LaboratoryNational Taiwan University
Institute of Information ScienceAcademia Sinica, Taiwan
INFOCOM, 2009
Network and Systems Laboratorynslab.ee.ntu.edu.tw
MotivationVoice traffic is sensitive to network
impairmentWhy VoIP sending rate is important?Most important factors on user satisfaction
Sending Rate and its VariationHigh and Stable voice quality
Why adapting sending rate is difficult?Aggressively?Conservatively?
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Motivation – Cont.Skype – one of the most popular VoIP
software
Q1: How Skype adapts its voice traffic?
Q2: Is their mechanism good enough?
Q3: How can Skype’s policy be improved?
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Related WorkSkype’s voice traffic is governed by: [Bonfiglio et al.]
Bit RateFraming TimeRedundant Data
PC-PSTN callsG.729
PC-PC calls iSAC
Only Redundant Data is controlled by Skype
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivationRelated WorkHow does Skype adapt the redundancy ratio?Is Skype’s mechanism good enough?How can we do better?Conclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivationRelated WorkHow does Skype adapt its redundant data?Is Skype’s mechanism good enough?How can we do better?Conclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Experiment Setup
PC-PC(iSAC)
PC-PSTN(G.729)
Only observing UDP sessions Voice Input : American English Speech Samples from Open Speech Repository
Network and Systems Laboratorynslab.ee.ntu.edu.tw
ObservationG.729 (PC-PSTN)
Constant bit rateConstant framing
time
2%
0%1%
0%
3%4%
5%6%
7%8%
9%10%
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Redundancy RatioDefinition
The percentage of packets that carry redundant voice data
1234
Redundancy Ratio = 2/4 = 0.5
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Estimate Redundancy Ratio of G.729
2%
0%1%
0%
3%4%
5%6%
7%8%
9%10%
the latter is used in Taiwan and Hong Kong, and the former is used more often in Mainland
Set Threshold at 40 bytes
G.729 (PC-PSTN)Constant bit rateConstant framing
time
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Identify Redundancy RatioRedundancy Ratio of G.729 (PC-PSTN Calls)
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Identify Redundancy RatioRedundancy Ratio of iSAC (PC-PC Calls)
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivationRelated WorkHow does Skype adapt its redundancy ratio?Is Skype’s mechanism good enough?How can we do better?Conclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Skype’s Redundancy Control Algorithm
Adapt to network loss rateAdapt to other factors?
CodecNetwork Loss Burstiness
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Effect of Network Loss BurstinessG.729 (PC-PSTN)
BR=1
BR=1.5
BR=2
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivationRelated WorkHow does Skype adapt its redundancy ratio?Is Skype’s mechanism good enough?How can we do better?Conclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Optimal Redundancy Control PolicyWhat’s the Optimal Policy?
Minimum amount of redundancy data we need to sustain the same audio quality under different network conditions
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Optimal Redundancy for the Burst Ratio
G.729, MOS=3.5
BR=1
BR=1.5BR=2
Skype
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Modeling Optimal Redundancy RatioBased on the targeted voice qualityTake codec and burstiness into
considerationOptimal Policy for G.729, targeted MOS=3.5
Network and Systems Laboratorynslab.ee.ntu.edu.tw
ConclusionExplore how Skype adapts its voice traffic
Redundancy RatioSkype’s policy does not factor in the individual
codec and loss patterns in to considerationPropose a general model for optimal policy
Consistent user satisfactionExtensible to general VoIP software